1. Field of the Invention
This invention relates to communication switching systems and more particularly to central office network configuration; and control and supervision therefor including search procedures for idle paths therein.
2. Description of the Prior Art
It is well known in switching system network arrangements that the probability of blocking can be reduced by the provision of additional switching stages or by increasing the number of attempts for a successful communication path. From the practical point of view, switching networks with an arbitrarily large number of switching stages require a very complex and expensive common control for path searching. Also, in actual practice, the number of attempts for a successful path in the nonfolded network is limited by the number of outgoing circuits provided. Additional limitation on the number of attempts is imposed when electromechanical markers are employed for path searching and real time expended per call is an important factor. Accordingly, a need exists for a switching network comprised of a practically manageable number of switching stages and capable of searching for all possible alternatives for a successful communication path.
Telecommunication networks are usually designed for ultimate maximum size. Initial networks are, in general, much smaller than the maximum size. When the network grows by the addition of lines or trunks, it is desirable to have minimum interruptions of service during the transition period. The conventional symmetric networks require a large amount of rearrangement. Therefore, a need also exists for a network which can grow from the initial size to the ultimate size in incremental steps on an in-service basis.